This invention relates to omega-hydrofluoroalkyl ethers and their preparation and application. In another aspect, this invention relates to perfluoro(alkoxyalkanoic) acids and derivatives thereof and their preparation. In another aspect, it relates to the preparation of perfluoro(alkoxyalkanoic) acids by direct fluorination of their hydrocarbon alkanoic acid or ester analogs and to the preparation of omega-hydroflouroalkyl ethers, for example, by decarboxylation of said acids or their alkyl esters. In another aspect, this invention relates to uses of perfluoro(alkoxyalkanoic) acids and derivatives thereof.
Because of a steady flow of bad news about the damaged stratospheric ozone layer, the deadlines for the end to industrialized countries"" production of chlorofluorocarbons (xe2x80x9cCFCsxe2x80x9d) and other ozone-depleting chemicals were accelerated by countries who are parties to the Montreal Protocol on Substances That Deplete the Ozone Layerxe2x80x94see Zurer, P. S., xe2x80x9cLooming Ban on Production of CFCs, Halons Spurs Switch to Substitutes,xe2x80x9d Nov. 15, 1993, Chemical and Engineering News, p. 12.
Work is under way to replace CFCs and halons, such as CCl2F2, CCl3F, CF3Br, and CCl2FCClF2, with substitute or alternative compounds and technologies. A number of hydrofluorocarbons (xe2x80x9cHFCsxe2x80x9d), e.g., CH2FCF3 (xe2x80x9cHFC-134axe2x80x9d), are being used or have been proposed as CFC substitutes (and HFC-134a has been characterized as being more xe2x80x9cozone friendlyxe2x80x9dxe2x80x94see U.S. Pat. No. 5,118,494 (Schultz et al.)). Hydrochlorofluorocarbons (xe2x80x9cHCFCsxe2x80x9d), such as CH3CCl2F (xe2x80x9cHCFC-141b), as the CandEN article, sura, points out, are CFC substitutes, but although they are not nearly as damaging, these substitutes do carry ozone-depleting chlorine into the stratosphere. Another proposed substitute is the simple omega-hydrodifluoromethyl perfluoromethyl ether, CF3OCF2Hxe2x80x94See J. L Adcock et.al., xe2x80x9cFluorinated Ethersxe2x80x94A new Family of Halons,xe2x80x9d 1991 CFC Conference Proceedings (1991). Another hydro-fluoroalkyl ether (or ether hydride), F[CF(CF3)CF2O]4CFHCF3, made by decarboxylation of the fluorinated 2-alkoxypropionic acid salt, has been tested as a blood emulsionxe2x80x94see Chem. Pharm. Bull. 33, 1221 (1985).
U.S. Pat. No. 4,173,654 (Scherer) states that fluorocarbons due to their inertness have found use as electronic coolant or leak testing fluids, and other compounds having good solubility for oxygen have been investigated as artificial blood substitutes. This patent describes certain fluorocarbon xe2x80x9chybridxe2x80x9d materials with metabolically active hydrocarbon moieties, such as, inter alia, xe2x80x94CH2xe2x80x94(CH2)mxe2x80x94H. U.S. Pat. No. 4,686,024 (Scherer et al.), which describes certain perfluorocyclic ethers, states that various perfluoro chemicals are disclosed in patents as being suitable as oxygen and carbon dioxide carriers. And International Application published as WO 93/11868 (Kaufman et al.) describes certain chlorofluorochemicals and emulsions thereof as useful in various oxygen transport applications, e.g., as oxygen transfer agents or xe2x80x9cartificial bloods.xe2x80x9d
There are a number of other patents describing various fluorocarbon ethers or polyethers. U.S. Pat. No. 3,342,875 (Selman et al.) describes certain xe2x80x9chydrogen modified fluorocarbon ethersxe2x80x9d (or xe2x80x9chydrogen capped polyethersxe2x80x9d) made, inter alia, by pyrolysis of a hydrogen-containing derivative of an ether, such as the fluorocarbon ether acid or the ammonium salt, which ether is obtained by the polymerization of fluorocarbon epoxides. British Patent Specification 1,194,431 (Montecatini Edison S.P.A.) describes certain perfluorinated ethers and polyether derivatives having the general formula
CF3xe2x80x94Oxe2x80x94(C3F6O)Mxe2x80x94(CF2O)Nxe2x80x94(CF(CF3)xe2x80x94O)Lxe2x80x94CF2X
where, inter alia, each subscript M, N, and L is zero or a whole number from 1 to 99, and X is a hydrogen atom or xe2x80x94COOMe wherein Me is an equivalent of an alkali or alkaline earth metal, an examples of which is pentafluorodimethyl ether, CF3xe2x80x94Oxe2x80x94CF2H.
U.S. Pat. No. 3,597,359 (Smith) describes certain perfluoroalkylene ether-containing compound represented by the formula 
wherein, inter alia, R is alkylene, alkoxyalkylene, or perfluoroalkylene, R1 is fluorine or trifluoromethyl provided not more than one R1 is trifluoromethyl, R2 is fluorine or trifluoromethyl provided not more than one R2 is trifluoromethyl, R3 is fluorine or trifluoromethyl, R4 is hydrogen or halogen provided that when R is alkylene or alkoxyalkylene R4 is hydrogen, R5 is perfluoroalkylene having at least 2 carbon atoms, R6 is, inter alia hydrogen, trifluoromethyl or perfluoroethyl, a is zero or 1, n and m are whole numbers of 0 to 50, and n+m is 1 to 50.
U.S. Pat. No. 3,962,460 (Croix et al.) describes aliphatic ethers, including those of the formulas 
International Patent Application WO 90/01901 (Long) describes certain perfluorocarbon hydrides, such as perfluorooctyl hydride, used in emulsions for carrying oxygen to the tissues of an animal body. European Patent Application Publication No. 0 482 938 A1 (Chambers et al.) describes fluorinated ethers of the formula 
wherein R is hydrogen, fluorine, or alkyl or fluoroalkyl of 1-6 carbon atoms, Rxe2x80x2 is hydrogen or alkyl or fluoroalkyl of 1 to 6 carbon atoms, and Rxe2x80x3 is fluorine or alkyl or fluoroalkyl of 1 to 6 carbon atoms.
Other patents describing one or more various fluoroalkoxyalkanoic acids and esters or other derivatives thereof and their preparation are U.S. Pat. No. 2,713,593 (Brice et al.), U.S. Pat. No. 3,214,478 (Milian, Jr.), U.S. Pat. No. 3,393,228 (Braun), U.S. Pat. No. 4,118,421 (Martini), U.S. Pat. No. 4,357,282 (Anderson et al.), U.S. Pat. No. 4,729,856 (Bernonge), U.S. Pat. No. 4,847,427 (Nappa), U.S. Pat. No. 4,940,814 (Schwertfeger), U.S. Pat. No. 4,973,716 (Calini et al.), U.S. Pat. No. 5,053,536 (Bierschenk et al.) U.S. Pat. No. 5,093,432 (Bierschenk et al.), and U.S. Pat. No. 5,118,494 (Schultz et al.) and PCT International Applications Pub. Nos. WO 90/03357 (Moore et al.) and WO 90/06296 (Costello et al.). The aforementioned Brice et al. patent describes fluorocarbons acids made by electrochemical fluorination including an acid having a boiling point of 225xc2x0 C. and said to be n-C8F17OC2F4CO2H. The aforementioned Nappa, Bierschenk et al., Moore et al., and Costello et al. publications describe the preparation of the fluorinated compounds by direct fluorination of hydrocarbon analog precursors.
In one aspect, this invention provides a normally liquid (i.e., liquid under ambient conditions of temperature and pressure) fluoroalkyl ether compound or a normally liquid composition consisting or consisting essentially of a selected mixture of such compounds, said compound having a saturated perfluoroaliphatic chain of carbon atoms (e.g., 4 to 30) interrupted by one or a plurality (e.g., 2 to 8) of ether (or catenary, i.e., in-chain) oxygen atoms. The chain carbon atom at one end (hereafter called the proximal end) of the chain is bonded to a hydrogen atom (i.e., an omega-hydro substituent, or primary hydrogen atom) and two fluorine atoms, said proximal carbon atom being the carbon atom of a difluoromethyl group or moiety, xe2x80x94CF2H, which is directly bonded to another chain carbon atom, such as that of perfluoroalkylene chain segment, xe2x80x94CNF2N, or to a said ether-oxygen. The carbon atom at the other end of the chain (the distal end) is part of a distal group selected from the group consisting of a difluoromethyl, a difluorochloromethyl, xe2x80x94CF2Cl, a perfluoroalkyl substituted with a saturated alicyclic moiety, e.g., cxe2x80x94C6F11xe2x80x94, a straight-chain perfluoroalkyl, and a branched chain perfluoroalkyl. In a said compound where said proximal end of the chain terminates in a difluoromethyl group bonded to an ether-oxygen atom, then said straight-chain perfluoroalkyl has at least 6 chain carbon atoms, e.g., 6 to 16 chain carbon atoms, and said branched-chain perfluoroalkyl has at least 4 carbon atoms, e.g., 4 to 16 carbon atoms. Examples of such omega-hydro fluoroalkyl ether compounds are: 
If a said xe2x80x9cselected mixture,xe2x80x9d i.e., a predetermined mixture of selected omega-hydrofluoroalkyl ether compounds, is desired for a particular use, a said composition of this invention can be made consisting or consisting essentially of a mixture of two or more of said compounds each having a desired discrete, non-random molecular weight, the selected compounds preferably being those having complementary properties, e.g., for imparting improved stability to emulsions where they are incorporated as oxygen carriers in medical applications.
The term xe2x80x9cperfluoro,xe2x80x9d such as in the case of xe2x80x9cperfluoroaliphatic,xe2x80x9d xe2x80x9cperfluoroalkylene,xe2x80x9d or xe2x80x9cperfluoroalkyl,xe2x80x9d means that except as may be otherwise indicated there are no carbon-bonded hydrogen atoms replaceable with fluorine nor any unsaturation.
Omega-hydrofluoroalkyl ethers of this invention are hydrophobic and less oleophobic than the perfluoroalkyl ether analogs, chemically inert, thermally stable, water insoluble, and normally liquid (e.g., at 20xc2x0 C.), and they can be made in accordance with this invention in high yield, high purity, and with a wide range of molecular weights. The covalent bond between the omega-hydrogen and terminal carbon, i.e., the Cxe2x80x94H bond, is generally degradable by atmospheric photo-oxidation, thus making the omega-hydrofluoroalkyl ethers environmentally acceptable or compatible. The omega-hydrofluoroalkyl ether compounds, or the normally liquid composition consisting or consisting essentially thereof, can be used in applications where the aforementioned CFCs, HCFCs or halons have been used, for example, as solvents for precision or metal cleaning of electronic articles such as disks or circuit boards, heat transfer agents, coolants in refrigerator or freezer compressors or air conditioners, blowing agents or cell size regulators in making polyurethane foam insulation, or chemical fire extinguishing agents in streaming applications, total flooding, explosion suppression and inertion, and as carrier solvents for highly fluorinated polyethers used as lubricants for magnetic recording media. Another field of utility for the omega-hydrofluoroalkyl ethers is in emulsions useful in various medical and oxygen transport applications, for example, artificial or synthetic bloods.
The above-described omega-hydrofluoroalkyl ethers of this invention can be prepared by decarboxylation of the corresponding precursor fluoroalkyl ether carboxylic acids and salts thereof or, preferably, the saponifiable alkyl esters thereof. Alternatively, the omega-hydrofluoroalkyl ethers can be prepared by reduction of the corresponding omega-chlorofluoroalkyl ethers (e.g., those described in WO 93/11868, supra). The perfluoroalkyl ether carboxylic acids (and esters) themselvesxe2x80x94some of which are believed novel compounds and they and their preparation are other aspects of this inventionxe2x80x94can be prepared by direct fluorination of their corresponding hydrocarbon analogs. The omega-hydrofluoroalkyl ethers are essentially pure fluorinated compounds and are useful as such or in the form of a normally liquid composition consisting or consisting essentially of a selected mixture of such compounds. The precursor perfluoroalkyl ether carboxylic acid and ester compounds, like the above-described omega-hydrofluoroalkyl compounds of this invention, have a saturated perfluoroaliphatic chain of a plurality of carbon atoms, said chain likewise being interrupted by one or a plurality of ether oxygen atoms, the proximal end of the chain being connected to a carboxyl group or alkyl ester thereof. This carboxyl group (or salts thereof or its saponifiable alkyl ester) can be decarboxylated, as mentioned above, and thereby replaced by the aforementioned omega-hydro substituent of the resulting omega-hydroalkyl ether of this invention.
The aforementioned novel perfluoroalkyl ether acids and esters can also be converted into various other derivatives, such as their ammonium salts, which have utility as surface active agents useful in modifying the surface tension or interfacial tension of liquids. These compounds are more soluble in aqueous media and other organic solvents than are the corresponding perfluoroalkanoic acid derivatives, and this enhances their utility as surface-active agents. The compounds can conveniently be prepared by direct fluorination of the corresponding hydrocarbon ether acids, or derivatives such as an ester, in high yields as single molecular species.
A class of the normally liquid, omega-hydrofluoroalkyl ether compounds of this invention can be represented by the general formula:
Xxe2x80x94Rfxe2x80x94Oxe2x80x94(Rfxe2x80x2xe2x80x94O)nxe2x80x94Rfxe2x80x3xe2x80x94Hxe2x80x83xe2x80x83I
wherein:
H is a primary hydrogen atom;
X is a fluorine atom, a primary hydrogen atom, or a primary chlorine atom bonded to a difluoromethylene (of Rf);
n is a integer of 0 to 7, preferably 0 to 3;
Rf, Rfxe2x80x2, and Rfxe2x80x3 are the same or different perfluoroalkylene (linear or branched) groups, e.g., xe2x80x94CF2CF2xe2x80x94, which are unsubstituted or substituted with a perfluoro organo group which can contain ether oxygen, for example, Rf can be xe2x80x94CF2CF(Rfxe2x80x2xe2x80x3)CF2xe2x80x94 or xe2x80x94Rfxe2x80x2xe2x80x3CF2xe2x80x94 where Rfxe2x80x2xe2x80x3 is a saturated perfluoroalicyclic group having 4 to 6 ring carbon atoms, such as perfluorocyclohexyl or perfluorocyclohexylene;
with the proviso that when X is H or Cl, Rf has 1 to 18, preferably 2 to 18, chain carbon atoms, Rfxe2x80x2 has 1 to 12, preferably 2 to 12, chain carbon atoms, and Rfxe2x80x3 has 2 to 12 chain carbon atoms;
and with the further proviso that when X is F, then Rf has at least 4, preferably 4 to 18, chain carbon atoms, Rfxe2x80x2 has 1 or more, preferably 1 to 12, more preferably 2 to 12, chain carbon atoms, and Rfxe2x80x3 has 2 or more, preferably 2 to 12, chain carbon atoms.
A subclass of polyether compounds within the scope of general formula I is represented by the general formula:
Xxe2x80x94Rfxe2x80x94Oxe2x80x94(CF2CF2xe2x80x94O)mxe2x80x94Rfxe2x80x3xe2x80x94Hxe2x80x83xe2x80x83II
where m is an integer of 0 to 7, and H, X, Rf, and Rfxe2x80x3 are as defined for formula I.
Another subclass of compounds within the scope of general formula I is represented by the general formula:
Fxe2x80x94Rfxe2x80x94Oxe2x80x94(Rfxe2x80x2xe2x80x94O)pxe2x80x94Rfxe2x80x3xe2x80x94Hxe2x80x83xe2x80x83III
where p is an integer of 0 to 2 and H, Rf, Rfxe2x80x2, and Rfxe2x80x3 are as defined for formula I, except Rf has 4 to 12 chain carbon atoms, Rfxe2x80x2 has 1 to 12 chain carbon atoms, and Rfxe2x80x3 has 2 to 12 chain carbon atoms.
Another class of the normally liquid, omega-hydrofluoroalkyl ether compounds of the invention can be represented by the general formula:
Xxe2x80x94Rfxe2x80x94O"Parenopenst"Rfxe2x80x2xe2x80x94O"Parenclosest"nRfxe2x80x3xe2x80x94H
wherein:
H is a primary hydrogen atom;
X is a fluorine atom, a primary hydrogen atom, or a primary chlorine atom;
n is an integer of 0 to 7; and
Rf, Rfxe2x80x2, and Rfxe2x80x3 are independently selected from the group consisting of linear or branched, unsubstituted perfluoroalkylene groups; linear or branched, perfluoroalkylxe2x80x94or perfluorocycloalkyl-substituted perfluoroalkylene groups; and linear or branched perfluoroalkylene groups substituted with an ether oxygen-containing moiety;
with the proviso that when X is H or Cl, Rf has 1 to 18 chain carbon atoms and each of Rfxe2x80x2 and Rfxe2x80x3 independently has 1 to 12 chain carbon atoms;
and with the further proviso that when X is F, then Rf has at least 4 chain carbon atoms and each of Rfxe2x80x2 and Rfxe2x80x3 independently has 1 or more chain carbon atoms;
and with the still further proviso that when n is zero, then Rf is a perfluorocycloalkyl-substituted perfluoroalkylene group.
A list of representative examples of the omega-hydrofluoroalkyl ether compounds of this invention is as follows.
As mentioned above, the omega-hydrofluoroalkyl ether compounds or compositions of this invention can be made by decarboxylation of their corresponding precursor perfluoroalkyl ether carboxylic acids, hydrolyzable carboxylic acid derivatives, or hydrolyzable precursors thereto (some of which are believed novel). A class of such precursor compounds can be represented by the general formula:
Rfpxe2x80x94O"Parenopenst"Rfxe2x80x2O"Parenclosest"nRfxe2x80x3xe2x80x94Zxe2x80x2xe2x80x83xe2x80x83IV
wherein
Rfp is ROC(O)Rf or Fxe2x80x94Rf, Rf being a perfluoroalkylene group as defined for formula I;
Rfxe2x80x2 and Rfxe2x80x3 are also perfluoroalkylene groups as defined for formula I;
n is also as defined for formula I; and
Zxe2x80x2 is a CO2H, CO2R, COF, COCl, CONR1R2, or xe2x80x94CF2OC(O)Rf, where R is selected from the group consisting of hydrogen, alkyl (such as a lower alkyl group of 1 to 6 carbon atoms), cycloalkyl, fluoroalkyl, and aryl, and where R1 and R2 are independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, and heteroatom-containing cycloalkyl.
In the decarboxylation of the compounds of formula IV, the moiety Zxe2x80x2 is replaced by a hydrogen atom.
Subclasses of said ether acids and derivatives thereof, which have other utilities in addition to their use as precursors of the omega-hydro ether compounds of this invention, for example, as surface active agents (or surfactants), as mentioned above, and which are believed novel, can be represented by the general formulas V, VI, VII, VIII and IX below,
Rfoxe2x80x94Oxe2x80x94Rfoxe2x80x2xe2x80x94Zxe2x80x83xe2x80x83V
wherein:
Rfo is a perfluoroalkyl group (linear or branched) having, for example, 1 to 18 carbon atoms, preferably 1 to 12 carbon atoms,
Rfo is a perfluoroalkylene group (linear or branched) having, for example, 2 to 11 carbon atoms, at least one of Rfo and Rfoxe2x80x2 having at least 8 chain carbon atoms; and
Z is xe2x80x94COOH, xe2x80x94COOMl/v, xe2x80x94COONH4, xe2x80x94COOR, xe2x80x94CH2OH, xe2x80x94COF, xe2x80x94COCl, xe2x80x94CR, xe2x80x94CONRR, xe2x80x94CH2NH2, xe2x80x94CH2NCO, xe2x80x94CN, xe2x80x94CH2OSO2R, xe2x80x94CH2OCOR, xe2x80x94CH2OCOCR=CH2, xe2x80x94CONH(CH2)mSi(OR)3, or xe2x80x94CH2O(CH2)mSi(OR)3, where M is an ammonium radical or a metal atom having a valence xe2x80x9cvxe2x80x9d of 1 to 4, such as Na, K, Ti, or Al, and each R is independently an alkyl (e.g., with 1 to 14 carbon atoms) or cycloalkyl, which groups can be partially or fully fluorinated, or an aryl (e.g., with 6 to 10 ring-carbon atoms), any of which groups can contain heteroatom(s), and m is an integer of 1 to about 11.
Rfq"Parenopenst"Oxe2x80x94CF2CF2"Parenclosest"aOCF2xe2x80x94Zxe2x80x83xe2x80x83VI
wherein:
Rfq is a perfluoroalkyl group (linear or branched) having from about 6 to about 18 carbon atoms, preferably 6 to 12 carbon atoms,
subscript a is an integer of at least 2, preferably 3 to 7, but when a is 2, then Rfq has at least about 8 carbon atoms; and
Z is as defined for formula V.
Rfrxe2x80x94Oxe2x80x94CF2xe2x80x94Oxe2x80x94Rfrxe2x80x2xe2x80x94Zxe2x80x83xe2x80x83VII
wherein:
Rfr is a perfluoroalkyl group (linear or branched) having, for example, 2 to 18 carbon atoms, preferably 4 to 12 carbon atoms;
Rfrxe2x80x2 is a perfluoroalkylene group (linear or branched) having, for example, 1 to 11 carbon atoms and preferably 1 to 5 carbon atoms; and
Z is as defined for formula V; and the sum of the number of carbon atoms in the groups Rfr and Rfrxe2x80x2 is at least about 7.
Rfsxe2x80x94O"Parenopenst"CF2"Parenclosest"bxe2x80x94Zxe2x80x83xe2x80x83VIII
wherein:
Rfs is a perfluoroalkyl group (linear or branched) having, for example, 1 to 18 carbon atoms, preferably 1 to 12 carbon atoms;
b is an integer of at least 3, preferably 3 to 11; and
Z is as defined for formula V.
Rftxe2x80x94(Oxe2x80x94Rftxe2x80x2)cxe2x80x94Oxe2x80x94(CF2)dxe2x80x94Zxe2x80x83xe2x80x83IX
wherein:
Rft is a perfluoroalkyl group (linear or branched) having, for example, 1 to 18 carbon atoms, preferably 1 to 12 carbon atoms;
Rftxe2x80x2 is a perfluoroalkylene group (linear or branched) having, for example, 1 to 11 carbon atoms, preferably 2 to 4 carbon atoms;
c is an integer of at least 1, preferably 1 to 4;
d is an integer of 3 or greater, preferably 3 to 9; and
Z is as defined for formula V.
The carboxylic acids of formulas V to IX are useful intermediates for the preparation of many of the other derivatives of formulas V to IX. These derivatives include nonfunctional or functional derivatives such as, for example, carboxylic acids, salts, esters, amides, nitrites, alcohols, acrylates, and vinyl ethers. Various patents describe processes for the preparation of a host of functional derivatives of oxyperfluoroalkylene compounds, i.e., perfluoropolyethers, e.g., see U.S. Pat. No. 3,250,808 (Mitsch et al.) and U.S. Pat. No. 4,094,911 (Moore et al.), which descriptions are incorporated herein. These derivatives have utility for various applications, such as surfactants, elastomers, coatings, lubricants, substances used in the preparation of liquid crystal materials such as those in U.S. Pat. No. 5,262,082 (Janulis et al.), and in the treatment of fibrous substrates to impart oil and water repellency thereto. The ammonium salts of the carboxylic acid derivatives are particularly useful as surfactants.
The carboxylic acid compounds of formula V are normally solid. The carboxylic acid compounds of formulas VI, VII, VIII and IX generally are normally liquid and normally liquid compositions can be made up which consist or consist essentially of selected mixtures of such compounds.
A list of representative examples of fluoroalkylether acids (or derivatives) which can be utilized to prepare omega-hydrofluoroalkyl ethers of this invention is as follows:
The following presents overall schemes of reactions that can be used in the preparation of omega-hydrofluoroalkyl ethers of this invention using general formulas defined above. In these schemes, the illustrated reaction results in the product whose formula is depicted on the succeeding line 
The ether alpha and omega dihydrides, that is, where X in formula I is H, may be prepared by analogous schemes. For example, the following Scheme IV is analogous to Scheme I 
Looking first at Scheme I above, in the direct fluorination, step xe2x80x9caxe2x80x9d, a fluorinatable precursor ether carboxylic acid ester, e.g., C4H9xe2x80x94Oxe2x80x94(CH2)5COOCH3, is directly fluorinated by contact with fluorine gas. (The term xe2x80x9cfluorinatablexe2x80x9d means that the precursor contains carbon-bonded hydrogen atoms which are replaceable with fluorine and the precursor may contain unsaturation which can be saturated with fluorine.) The resulting fluorinated ether acid ester compound, depicted in step b, can be made with essentially the same number and spatial arrangement of carbon and oxygen atoms as the precursor thereof. If a fluorinated ether acid composition which consists or consists essentially of a selected mixture of fluorinated ether compounds is desired, a selected mixture of the corresponding precursor compounds can be fluorinated or, alternatively, the selected precursor compounds can be separately fluorinated and then blended.
The direct fluorination of the fluorinatable ether precursor can be carried out at temperatures typically used in direct fluorination, e.g., at moderate or near ambient temperatures such as xe2x88x9220xc2x0 C. to +50xc2x0 C., using a stoichiometric excess of fluorine gas, which is preferably diluted with an inert gas, such as nitrogen, to minimize or avoid the hazards of pure fluorine gas and to control the amount of heat generated upon contact of the precursor with fluorine. The fluorination is preferably carried out in an oxygen- and water-free environment and can be carried out in the presence of solid, particulate scavenger, e.g., sodium fluoride, for the hydrogen fluoride by-product generated. Liquid phase direct fluorination can be employed and involves using an inert liquid, such as a fluorocarbon or chlorofluorocarbon liquid, as a reaction medium. Both scavenger and an inert liquid reaction medium can be utilized, if desired. The fluorination is preferably carried out by liquid phase direct fluorination in the absence of hydrogen fluoride scavenger by using a temperature and inert gas flow rate sufficient to volatilize hydrogen fluoride by-product and enable its removal from the fluorination zone as it is generated.
In another aspect, this invention provides a fluorochemical composition containing the fluorinated ether acid or derivative thereof, hereinbefore described, as the sole essential component of the fluorochemical composition.
Although direct fluorination is a substitution method involving the replacement of hydrogen atoms with fluorine, direct fluorination provides higher yields and purer products than do other substitution methods such as the electrochemical fluorination and cobalt trifluoride methodsxe2x80x94see, for example, U.S. Pat. No. 5,093,432 (Bierschenk et al.). The purity of the perfluorinated ether acid (or ester) compositions of the invention is further enhanced by the use of single precursor compounds or selected (rather than random) mixtures thereof.
The preferred method of fluorination is the xe2x80x9cliquid phase direct fluorination technique,xe2x80x9d which involves making a very dilute dispersion or, preferably, solution of the precursor(s) in a liquid reaction media, which is relatively inert to fluorine at the fluorination temperatures used, the concentration of fluorinatable starting material thus being relatively low so as to more easily control the reaction temperature. The reaction mixture can also contain or have dispersed therein a hydrogen fluoride scavenger such as sodium fluoride, the scavenger:precursor weight ratio being, for example, from about 0.5:1 to 7:1. The reaction mixture can be vigorously agitated while the fluorine gas is bubbled through it, the fluorine preferably being used in admixture with an inert gas, such as nitrogen, at a concentration of about 5 to 50 volume %, more preferably about 10 to 25 volume %, and being maintained in stoichiometric excess throughout the fluorination, e.g., up to 15 to 40%, or higher, depending on the particular starting material and the efficiency of the equipment used, such as the reactor agitation. Yields generally in the range of about 30-77 mole %, and, with experience, as high as 65 to about 85 mole %, of the perfluorinated product may be achieved by this method.
Suitable liquids useful as reaction media for the liquid phase direct fluorination technique are chlorofluorocarbons such as Freon(trademark) 11 fluorotrichloromethane; chlorofluoroethers; Fluorinert(trademark) electronic liquids FC-75, FC-72, and FC-40; perfluoroalkanes such as perfluoropentane and perfluorodecalin; perfluoropolyethers; and perfluoroacetals. Mixtures of such liquids can be used, e.g., to get good dispersion of precursor and intermediate reaction products. The reaction media are conveniently used at atmospheric pressure. Lower molecular weight members of the above classes of reaction media can also be used, but elevated pressures are then required to provide a liquid phase.
The liquid phase direct fluorination reaction is generally carried out at a temperature between about xe2x88x9210xc2x0 C. to +50xc2x0 C., preferably between about xe2x88x9210xc2x0 C. to 0xc2x0 C. if a hydrogen fluoride scavenger is used, and, if such a scavenger is not used, between about 0xc2x0 C. to 150xc2x0 C., preferably about 0xc2x0 C. to 50xc2x0 C., most preferably about 10xc2x0 C. to 30xc2x0 C., the temperature being sufficient to volatilize the hydrogen fluoride by-product and, with the aid of the inert gas, flowing at a sufficient rate, cause the purging of the by-product from the fluorination reactor as it is generated. At these temperatures, the liquids utilized as reaction media do not react appreciably with the diluted fluorine and are essentially inert. The reaction medium and other organic substances may to some extent be present in the gaseous reactor effluent, and a condenser may be used to condense the gaseous reaction medium and such substances in the effluent and permit the condensate to return to the reactor. The condenser can be operated so as to minimize or prevent the return to the reactor of hydrogen fluoride by-product (which could have an adverse effect on yield of product if allowed to remain in the reactor during fluorination). The return of the hydrogen fluoride can be minimized or prevented by selective condensation of the organic materials while allowing the hydrogen fluoride to pass through the condenser, or by total condensation of both hydrogen fluoride and the organic materials into a separate vessel and followed, if desired, by separation of the hydrogen fluoride as the upper liquid phase and the return of the lower liquid phase.
The liquid phase fluorination reaction may be carried out in a batch mode, in which all of the precursor is added to the liquid prior to fluorination to provide a precursor concentration of up to about 10% by weight, and the fluorine-containing gas is then bubbled through the precursor-containing liquid. The reaction can also be carried out in a semi-continuous mode, in which the precursor is continuously pumped or otherwise fed neat, or as a diluted solution or dispersion, in a suitable liquid of the type used as a reaction medium, into the reactor, e.g., at a rate of about 1 to 3 g/hr into 400 mL of liquid reaction mixture, as fluorine is bubbled through, e.g., at a fluorine flow rate of about 40 to 120 mL/min and an inert gas flow rate of about 150 to 600 mL/min. The fluorination can also be carried out in a continuous manner, in which the precursor (either neat or dissolved or dispersed in a suitable liquid of the type used as a reaction medium) is continuously pumped or otherwise fed into the reactor containing the reaction medium as the fluorine-containing gas is introduced, as described above, and the stream of unreacted fluorine, hydrogen fluoride gas, and inert carrier gas is continuously removed from the reactor, as is a stream of liquid comprising perfluorinated product, incompletely fluorinated precursor, and inert liquid reaction medium, and the necessary separations are made to recover the fluoroalkyl ether composition. If desired, the unreacted fluorine and the incompletely fluorinated precursor can be recycled. The amount of inert liquid medium in the reactor can be maintained at a constant level by addition of recycled or fresh liquid.
Due to the extremely high exothermicity of the fluorination reaction, a cooled liquid or ice bath is generally employed in order that acceptable rates of reaction may be achieved. When the reaction is complete, the reactor is purged of fluorine and the reactor contents are removed. Where the fluorination is carried out by the liquid phase fluorination technique in the presence of a hydrogen fluoride scavenger, the spent scavenger can be separated by filtration or decantation from the liquid reactor contents and the latter then distilled to separate the reaction medium from the crude product. Where the fluorination is carried out by the liquid phase fluorination technique without using the scavenger, the reaction product mixture can be distilled to recover the product.
Useful representative precursor fluorinatable ether acid esters which can be used to prepare the omega-hydrofluoroalkyl ethers of this invention are the hydrocarbon counterparts of the structures listed in Table A above, except that instead of the terminal hydrogen atom the structures of the esters terminate with xe2x80x94Zxe2x80x2 (where Zxe2x80x2 is as defined for formula IV) or xe2x80x94CH2OC(O)R (as shown in Scheme II supra) and that the precursors can contain unsaturation.
Representative examples of the fluoroether acids of or used in this invention include the perfluorinated (i.e., having essentially all hydrogens replaced with fluorine) counterparts of the precursor fluorinatable acid esters described above. When the precursors have unsaturation, the corresponding fluorinated ether acids are saturated.
As pointed out above, the fluoroether acids and derivatives can be used as precursors in the preparation of the omega-hydrofluoroalkyl ethers and they are also useful, for example, as surfactants.
The above-described fluoroether acids or the esters thereof, e.g., alkyl esters such as the methyl ester, can be converted by a decarboxylation process to the omega-hydrofluoroalkyl ethers of this invention. In one such process, a solution of KOH in ethylene glycol is prepared and the fluoroether acid or ester precursor is added thereto (neat or as a solution in an inert solvent liquid such as a perfluorinated liquid), preferably dropwise with stirring at ambient or room temperature. The resulting mixture can then be heated slowly, for example, to 190xc2x0 C., during which time the methanol (from the saponification of a methyl ester), water (from neutralization of an acid), and decarboxylated product are distilled. The omega-hydrofluoroalkyl ethers of the invention are surprisingly stable under such harsh basic conditions. An inert solvent liquid, if used, can be removed, for example, at low temperature under vacuum after neutralization. The resulting distillate, comprising the omega-hydrofluoroalkyl ether product, can be washed with water, dried with silica gel or magnesium sulfate, and then distilled to purify the product. If desired, the hydrofluoroalkyl ether product can be refluxed with a solution of potassium permanganate in acetone to remove easily-oxidized impurities. The yields of the ether product are generally high and the product generally will be quite pure and consist or consist essentially of the desired omega-hydrofluoroalkyl ether.
The omega-hydrofluoroalkyl ether compositions are non-toxic and capable of dissolving and transporting oxygen and are therefore potentially useful as blood substitutes which can be employed invasively in the treatment of trauma, vascular obstructions, as adjuvants to cancer radiation treatment or chemotherapy, and as imaging contrast agents. For such uses, emulsions of the compositions can be prepared by methods such as those described, for example, in U.S. Pat. No. 3,911,138 (Clark) and U.S. Pat. No. 5,077,036 (Long) and the PCT International Application published as WO 93/11868 (Kaufman et al.), which descriptions are incorporated herein by reference. The omega-hydrofluoroalkyl ether compositions are also useful as solvents for cleaning and drying applications such as those described in U.S. Pat. No. 5,125,089 (Flynn et al.), U.S. Pat. No. 3,903,012 (Brandreth), and U.S. Pat. No. 4,169,807 (Zuber). Minor amounts of optional components, e.g., surfactants, may be added to the fluoroether compositions to impart particular desired properties for particular uses. The ether compositions are also useful as heat transfer agents or coolants in refrigerator or freezer compressors or air conditioners, blowing agents or cell size regulators in making polyurethane foam insulation, or chemical fire extinguishing agents in streaming applications, total flooding, explosion suppression and inertion, and as carrier solvents for highly fluorinated polyethers used as lubricants for magnetic recording media.
In using the omega-hydrofluoroalkyl ether compositions of this invention for the drying of or displacing water from the surface of articles, such as circuit boards, the processes of drying or water displacement described in U.S. Pat. No. 5,125,978 (Flynn et al.) can be used. Broadly, such process comprises contacting the surface of an article with a liquid composition comprising the ether composition of this invention, preferably in admixture with a non-ionic fluoroaliphatic surface active agent. The wet article is immersed in the liquid composition and agitated therein, the displaced water is separated from the liquid composition, and the resulting water-free article is removed from the liquid composition. Further description of the process and the articles which can be treated are found in said U.S. Pat. No. 5,125,978, which description is incorporated herein.
In using the ether composition of this invention as a heat transfer liquid in vapor phase soldering, the process described in U.S. Pat. No. 5,104,034 (Hansen) can be used, which description is incorporated herein. Briefly, such process comprises immersing the component to be soldered in a body of vapor comprising the ether composition of this invention to melt the solder. In carrying out such a process, a liquid pool of the ether composition of this invention can be heated to boiling in a tank to form a saturated vapor in the space between the boiling liquid and a condensing means, a workpiece to be soldered is immersed in the vapor whereby the vapor is condensed on the surface of the workpiece so as to melt and reflow the solder, and the soldered workpiece is then removed from the space containing the vapor.
In using the ether composition of this invention as a blowing agent in making plastic foam, such as foamed polyurethane, the process reactants, and reaction conditions described in U.S. Pat. No. 5,210,106 (Dams et al.) can be used, which description is incorporated herein. In carrying out such process, organic polyisocyanate and high molecular weight compound with at least 2 reactive hydrogen atoms, such as a polyol, are admixed in the presence of a blowing agent mixture comprising an ether composition of this invention, catalyst, and a surfactant.
This invention is further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.